The present invention relates generally to a core of a magnetic head and a method of producing such a magnetic head core, and more particularly to a magnetic head core made of ferrite with a magnetic gap formed between core elements, and having substantially no rear or back gap opposite to the magnetic gap, ad to a method of manufacturing the same.
In the art of magnetic heads for various types of recording media, a core made of ferrite has been known, which generally consists of a pair of ferrite core elements joined together to form a structure of a ring-shaped or a toric cross section having a centrally located large aperture or void which facilitates winding of coils around the core elements. More specifically, referring to FIG. 1, which shows a common type of magnetic head core, a pair of generally C-shaped ferrite core halves 2, 4 are butted together to form the core with a central aperture 6 which serves as a space for winding coils 8 around the core halves 2, 4. In this manner, an annular or toric magnetic circuit is constituted by the two C-shaped ferrite core halves 2, 4. Additionally, the toric magnetic core structure is formed with a magnetic gap 10 at one end portion of the core. The gap 10 is formed to extend across the toric magnetic circuit and has a suitable width .alpha. which is the distance between the opposed end surfaces of the core halves 2, 4. As is well known in the art, a magnetic tape 12, magnetic disk or other magnetic recording medium, is slidably moved on outer contact surfaces of the core halves 2, 4 in the proximity of the gap 10 defined by these halves 2, 4, whereby magnetic writing (recording) and reading (reproducing) processes are effected.
As indicated above, the ends of the core halves 2, 4 at one end of the core have the opposed surfaces which are spaced apart from each other by a distance equal to the width .alpha. of the magnetic gap, while the other ends of the core halves 2, 4 are bonded together with suitable bonding glass so as to maintain a generally toric cross sectional shape of the magnetic core as a whole. In this known ferrite core formed of the two core elements 2, 4 bonded together with glass, however, it is inevitable that a very small gap 14, a so called rear gap or back gap, is formed between the bonded abutting surfaces of the core elements 2, 4. The existence of this rear gap 14, which is located opposite to the magnetic air gap 10 at the front of the core, necessarily increases the magnetic resistance of the magnetic circuit, and consequently has an adverse effect on the sensitivity, and signal to noise ratio (S/N ratio) of a magnetic head using the core, which sensitivity and S/N ratio are important characteristics of the magnetic head. In other words, it is required to completely eliminate the rear gap 14, i.e., to reduce the width of the gap to zero in order to maximize the sensitivity of the magnetic head, and accordingly improve the S/N ratio. However, this requirement has not been satisfied by any traditional ferrite core formed from a plurality of core members or elements as described above.
While the above-described type of ferrite core for a magnetic head is constructed of two core elements which are joined together to form a toric or a ring-shaped structure, an alternative method of producing such a ferrite core is known, which comprises press-molding an integral toroidal or ring-shaped body of ferrite and forming a magnetic gap of a suitable size in the molded ferrite body. In this alternative method, wherein the magnetic gap is formed in the toroidal molding of ferrite in a suitable mechanical process, the width .alpha. of the magnetic gap is necessarily greater than a certain limit. For example, when the magnetic gap is formed by sawing the molded ferrite body with a diamond cutter, the minimum possible width of the gap is about 0.3 mm, which is relatively large and only suitable for an erasing head.
On the contrary, the cores of magnetic heads for VTR and computer applications are required to have a comparatively small or narrow magnetic gap, the width .alpha. thereof ranging from 0.4 to 3 microns, approximately, for improved magnetic characteristics. However, a molded integral ferrite core with such a small magnetic gap width has not yet been obtained in this field of technology. Stated differently, the failure or incapability to provide a molded ferrite core with such a small magnetic gap (0.4-3 microns) has necessitated the use of a pair of ferrite core elements, as previously indicated, to produce a magnetic core for a magnetic disk, for example, which requires a very small magnetic gap.